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Full text of "Text Book Of Mechanical Engineering"

Appendix II.

839

attention to strengths at high temperatures, and he states that
iron and steel usually gain slightly in strength up to 500°, but
after 600° decrease rapidly. For the copper alloys he deduces
the maximum strength:

/ = a - b (t\ - 6o)2

where the values of a and b are as follows :


	a.
	b.

CoDDer
	14. "8
	'OOOOI4

Gun-metal (cast)  ...
	I 2X
	"OOOO5O

Phosphor Bronze (cast)   ... Brass (cast)
	A ^ 0
 16-1
 I 2*£
	•OOOO26 "OOOO24

Brass (rolled)        ...........
	A*  J 2 A' I
	•OOOO28

Delta Metal (rolled)         ......... Muntz Metal (rolled )       .........
	31*3
 24*7
	"OOOO4I "OOOO29

Experiments are made by surrounding the specimen with a
box of oil heated by gas-jets, the measuring apparatus being
outside. (Seej>. 1074.)

EXPERIMENT ON WHITWORTH COMPRESSED STEEL.
BY PROFESSOR GOODMAN.


	At 60° Fahr.
	At 400° Fahr.

Maximum stress per sq. in. Elastic limit per sq. in __        ... Extension in 10 ins.      ...        ...
	34'03 21-97
 16%
	31-83
 20-45
 "7%

P. 390. Wohler's Law.—Unwinds formula, p. 390, being
empirical, cannot be proved from first principles, so its application
will be further shewn in the next problem.

Example 62.—Two steel bars, having a static breaking load of 30
tons per square inch, are stressed in tension, the one from 5 to 6 tons
and the other from i to 6 tons per square inch. Find the actual breaking
strengths to be assumed for the respective methods of loading,